Floral Structure of Spuria Iris

Students of floral anatomy are often confused by the by the appearance of an Iris flower since it is specialized and unique in a number of ways. To understand the structure it is useful to have a background of how flowers evolved.
According to one theory the flower evolved as a leafy shoot possibly with sets of leaves in whorls or cycles. At the very tip of the shoot was a cycle of leaves that bore eggs and developed into the female parts known collectively as the gynoecium. The next cycle down (the androecium) was a set of leaves that bore pollen and developed into specialized male parts, followed by two more cycles; one which became colored attractive petals, collectively known as the corolla, and another which became a protective covering for the flower made up of what are known as sepals and collectively known as the calyx. The corolla and calyx are collectively known as the perianth. In Iris these two outer cycles appear as one cycle and we no longer refer to their parts as petals and sepals but now we use the term tepals.These four cycles are most easily visualized in primitive flowers such as waterlillys and buttercups.
In Iris the perianth is made up of two types of tepals, Standards towards the center and Falls that provide an outer layer in bud. These terms are easily understood in spuria Irises because the standards rise and the falls fall or at least flare outwards. At their base the standards and falls unite into the perianth tube, which is very short in spuria Irises but in some other types of Iris may elevate the flowers as if it were a stalk above the ovary.
One of the characteristics that makes Iris unique is the structure of the central cycle, the gynoecium. In our buttercup flowers there are many female structures known as pistals, each composed of an ovary, a style, and a stigma. the stigma is a surface that receives the pollen which grows down the style, which is a stalk connecting to the ovary which houses the eggs. In Iris these structures are totally different. We have only one ovary at the base of the flower and it has three chambers with eggs. The perianth tube comes off the top of the ovary along with the petal like styles which are termed stylearms. The tip of the stylearm has a crest with a flap of tissue below known as the stigmatic lip which receives pollen. The anthers are pressed against the stylearm underside and so not in sight but are just like a buttercup's.


 

-- Main.RPries - 2009-10-14
Topic revision: r1 - 14 Oct 2009, RPries
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